Compact Dry-Running Piston Compressor

ABSTRACT

A compact dry-running piston compressor includes at least one cylinder for the compression of air by a corresponding piston, which may be driven by an electric motor with a crank drive made up of a crankshaft and connecting rod. The crank drive is rotatably mounted in an oil-bath-free compressor housing on pre-lubricated roller bearings and generates an internal cooling air flow inside the housing due to its movement cycle. The compressor housing includes two housing sections separated by a partition wall, in order to accommodate the crank drive within the first housing half and the electric motor in the second housing half. A roller bearing common to the crank drive and the electric motor is arranged in the partition wall lying in the cooling air flow passing through the first housing half.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT International Application No. PCT/EP2008/006916, filed Aug. 22, 2008, which claims priority under 35 U.S.C. §119 from German Patent Application No. DE 10 2007 042 318.9, filed Sep. 6, 2007, the entire disclosures of which are herein expressly incorporated by reference.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to a compact dry-running piston compressor, particularly for commercial vehicles, having at least one cylinder for compressing air by way of an associated piston. The piston can be moved by electric motor via a crank drive composed of a crankshaft and a connecting rod, which crank drive is rotatably mounted by way of permanently lubricated roller bearings in a compressor housing which has no oil bath. The crank drive generates a cooling air flow within the housing as a result of the movement cycle.

The field of application of the present invention extends primarily to rail vehicle and commercial vehicle construction. Here, as auxiliary compressors, use is made of small electromotively driven units which produce compressed air for consumers or loads within the vehicle. In the past, use was made predominantly of oil-lubricated piston compressors for this purpose. Modern compressor concepts based on piston compressors also permit oil-free operation. Instead of the crankcase being filled with oil, the bearing points of the crank drive are in this case mounted using roller bearings, and the roller bearing arrangements are provided with local permanent lubrication. The oil-free piston compressor has been developed in particular for servicing and environmental reasons.

DE 10 2004 042 944 A1 discloses a generic dry-running piston compressor. The piston compressor is composed substantially of a compressor unit for producing compressed air, which compressor unit is driven by a drive unit for producing a rotational movement. Here, the drive unit is usually in the form of an electric motor. A crankshaft is rotatably mounted within the crankcase of the compressor unit. Two connecting rods are attached to the crankshaft, which connecting rods are connected to associated pistons in order to convert the drive-side rotational movement into a linear movement of the pistons which, in order to compress air, are accommodated within associated cylinders. Here, the cylinders are attached to the crankcase in a 180° position. To improve the cooling of the cylinders, an inlet-side valve is provided which moves into its open position in the event of a vacuum being produced in the crankcase by the movement of the piston. In this way, cooling air is sucked in from the outside, and at least one outlet-side valve, which is arranged spaced apart from the inlet-side valve on the crankcase, moves into its open position in the event of an excess pressure being produced in the crankcase by the movement of the piston. In this way, consumed cooling air is discharged such that an internal cooling air flow flows through the crankcase as a result of the movement cycle of the pistons.

Although the above technical solution utilizes a cooling air flow for the internal cooling of a dry-running piston compressor, the flange-mounted electric motor must be cooled separately, which usually takes place by means of a fan impeller on the electric motor. This again permits the infiltration of moisture and dirt from the environment. To prevent this, additional encapsulation of the piston compressor together with the electric motor has hitherto been provided, but this considerably increases the space requirements of the unit.

It is therefore an object of the present invention to provide a compact dry-running piston compressor suitable for use in contaminated environments and distinguished by a long service life.

This and other objects are achieved by a compact dry-running piston compressor having at least one cylinder for compressing air via an associated piston which can be moved by electric motor via a crank drive composed of a crankshaft and a connecting rod. The crank drive is rotatably mounted by way of permanently lubricated (pre-lubricated) roller bearings in a compressor housing which has no oil bath. The crank drive generates a cooling air flow within the housing as a result of the movement cycle. The compressor housing comprises two housing sections separated by a partition such that the crank drive is accommodated within the first housing section and the electric motor is accommodated within the second housing section. A roller bearing, which is common to the crank drive and to the electric motor, is inserted into the partition. The roller bearing is situated in the cooling air flow passing through the first housing section.

An advantage according to the invention is, in particular, that a common housing is provided for the compressor unit and for the drive, which housing ensures complete encapsulation with respect to contaminated environments. At the same time, the thermal problems arising with such encapsulation are solved overall for the compressor unit and for the drive unit by way of a common cooling air flow. The solution according to the invention can be accomplished because of the realization that the driven-side end of the motor windings is the decisive heat source, which can be efficiently cooled by way of local cooling measures in conjunction with a common housing. The solution according to the invention is optimized with regard to the required number of roller bearings. It is thus possible to use a single roller bearing jointly for the electric motor and the crankshaft mounting. If the single roller bearing is cooled in a targeted fashion, then an adequate cooling action is also obtained for the electric motor, which is made possible by way of the heat conduction in the region of the partition.

According to a preferred embodiment of the invention, at least one opening for branching or diverting parts of the cooling air flow of the first housing section into the second housing section is provided in the partition. In this way, the cooling air flow can be conducted in a targeted fashion also into the region of the second housing section, such that the cooling action can be improved using this measure.

The crankshaft is preferably rotatably mounted not only by way of the roller bearing arranged in the partition but also, at its other side, by way of a further roller bearing. A total of two roller bearings for the crankshaft is therefore adequate for rotatably mounting the crank drive together with the electric motor. Here, the further roller bearing can be inserted, so as to be encapsulated with respect to the outside, in a cover, which is flat in terms of its basic shape, of the first housing section. As a result of the flat cover, the external geometric dimensions of the piston compressor are not increased considerably. At the same time, the flat cover provides an easily dismountable facility for accessing the interior of the crankcase. The second roller bearing should likewise be situated in the cooling air flow passing through the first housing section.

To maximize compactness, it is proposed that the rotor of the electric motor be attached directly to an end, which projects into the second housing section, of the crankshaft. This attachment may take place by way of a conical flange with an end-side screw connection. However, it is also contemplated for the crankshaft and rotor to be formed in one piece. This is expedient in particular if the electric motor is in the form of a brushless electric motor whose rotor need merely be equipped with permanent magnets. In contrast, the stator is provided with electric coil windings.

The commutating electronics required for such a brushless electric motor which is preferably to be used here can likewise be integrated in a simple manner into the second housing section. The commutating electronics should preferably be arranged on a flat printed circuit board which is arranged in the region of the housing wall. For better accessibility to the commutating electronics, the latter may be closed off by a cover which can be screwed on. The second housing section is closed off at the end side by a cover which is likewise flat in terms of basic shape. After the cover has been mounted, the inner region of the electric motor is accessible for servicing and repair purposes.

The integrated compressor housing designed according to the invention also has, in the region of the first housing section, an opening for the releasable attachment of a cylinder, which is preferably formed as a separate component. As a result of the cylinder being formed separately, it is possible for the integrated compressor housing with the two housing sections or halves to be formed in a simple manner in terms of casting, preferably by means of light metal casting.

In one refinement of the invention, inflow ducts are provided in the piston compressor, the cross sections of which inflow ducts vary such that different cooling air flows flow through the individual assemblies. Here, the individual assemblies are the crankcase, the winding space of the electric motor and the commutating electronics. It is advantageous for the corresponding regions to be supplied optimally with a sufficient quantity of cooling air.

Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal section view through a compact dry-running piston compressor; and

FIG. 2 is a longitudinal section view through a compact dry-running piston compressor with inflow ducts.

DETAILED DESCRIPTION OF THE DRAWINGS

In FIG. 1, the compressor has a single cylinder 1 in which is arranged a piston 2 for compressing air sucked in from the environment via a cylinder head 3. The linear reciprocating working movement of the piston 2 is generated by a crank drive. The crank drive is composed essentially of a crankshaft 4 and a connecting rod 5. The crankshaft 4 is mounted so as to be rotatable with respect to the compressor housing 7 by way of two roller bearings 6 a and 6 b.

The compressor housing 7 is composed of a first housing section 8, such as a first housing half, which forms the crankcase, and a second housing section 9, such as a second housing half, which houses an electric motor 10. As used herein, the term housing “half” is not limited to an evenly divided housing.

In this exemplary embodiment, the electric motor 10 is in the form of a brushless electric motor and includes a stator 11 composed of coil windings with an iron core. The stator 11 interacts with a rotor 12, which is equipped with permanent magnets. The rotor 12 of the electric motor 10 is screwed onto a conical end of the crankshaft 4, which conical end projects into the second housing half 9. Commutating electronics 13 of the electric motor 10 are integrated in the wall of the second housing half 9. For a space-saving arrangement, the commutating electronics 13 are accommodated on one printed circuit board. The second housing half 9 is closed off by a flat cover 14 at the end side by use of individual screws. The first housing half 8 also has a cover 15, which is flat in terms of its basic shape and which closes off the housing half 8 at the end side also by use of screw connections.

The cover 15 of the first housing half 8 includes a seat for the roller bearing 6 a of the crankshaft 4. The other roller bearing 6 b of the crankshaft 4 is located in a partition 16 of the compressor housing 8. The roller bearing 6 b is provided both for mounting the crankshaft 4 at one side and also for mounting the rotor 12 of the electric motor 10.

The two roller bearings 6 a and 6 b are situated in a cooling air flow which passes through the first housing half 8. On account of the movement cycle of the crank drive, the cooling air flow passes, in a manner controlled by a valve, via a cylinder-side duct 17 into the interior of the first housing half 8 and leaves the latter through a valve-switched opening 18. Here, the cooling air flow is conducted through the first housing half 8 in such a way that the two roller bearings 6 a and 6 b are cooled. To deflect parts of the cooling air flow of the first housing half 8 into the second housing half 9, the partition 16 has a ring of openings 19.

FIG. 2 shows another embodiment in which inflow ducts 20 are provided. The inflow ducts 20 are supplied with air via the duct 17. These inflow ducts convey cooling air to the individual components, with the quantity of cooling air being defined by the respective cross sections. The flow of air is shown by the block arrows in FIG. 2.

The invention is not restricted to the preferred exemplary embodiments described above. For example, it is also possible for the electric motor to be of some other type. In principle, any type is suitable which can be accommodated, so as to be encapsulated, within the housing half 9.

Table of Reference Numerals 1 Cylinder 2 Piston 3 Cylinder head 4 Crankshaft 5 Connecting rod 6 Roller bearing 7 Compressor housing 8 First housing half 9 Second housing half 10 Electric motor 11 Stator 12 Rotor 13 Commutating electronics 14 Cover 15 Cover 16 Partition 17 Duct 18 Opening 19 Opening 20 Inflow ducts

The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof. 

1. A compact dry-running piston compressor having at least one cylinder for compressing air via an associated piston, the compressor comprising: a crank drive including a crankshaft and connecting rod, the connecting rod being connectable with the piston; an electric motor operatively configured to drive the associated piston via the crank drive; an oil-bath-free housing comprising first and second housing sections separated by a partition, the crank drive being accommodated within the first housing section and the electric motor being accommodated within the second housing section; and pre-lubricated roller bearings arranged in the housing for rotatably mounting the crank drive, one of said roller bearings being common to the crank drive and the electric motor and arranged in the partition, the one roller bearing being located in a cooling air flow generated by a movement cycle of the crank drive, which cooling air flow passes through the first housing section.
 2. The compact dry-running piston compressor according to claim 1, further comprising at least one opening provided in the partition, the at least one opening allowing at least a portion of the cooling air flow to be branched from the first housing half into the second housing half.
 3. The compact dry-running piston compressor according to claim 1, wherein the electric motor comprises a driven-side end winding, the driven-end side winding being concomitantly cooled via the one roller bearing located in the cooling air flow and via heat conduction of the partition.
 4. The compact dry-running piston compressor according to claim 2, wherein the electric motor comprises a driven-side end winding, the driven-end side winding being concomitantly cooled via the one roller bearing located in the cooling air flow and via heat conduction of the partition.
 5. The compact dry-running piston compressor according to claim 1, wherein a further roller bearing rotatably mounts the crankshaft, the further roller bearing arranged at another side of the crankshaft.
 6. The compact dry-running piston compressor according to claim 5, further comprising: a relatively flat cover operatively configured for closing the first housing section; and wherein the further roller bearing is arranged in the cover so as to be encapsulated with respect to the area outside of the cover.
 7. The compact dry-running piston compressor according to claim 5, wherein the further roller bearing is also located in the cooling air flow passing through the first Musing section.
 8. The compact dry-running piston compressor according to claim 5, wherein a rotor of the electric motor is mounted in the housing via two roller bearings of the crankshaft.
 9. The compact dry-running piston compressor according to claim 1, wherein a rotor of the electric motor is attached directly to an end of the crankshaft, said end of the crankshaft projecting into the second housing section.
 10. The compact dry-running piston compressor according to claim 1, wherein the electric motor is a brushless direct-current motor having a stator composed of coil windings with an iron core and a rotor equipped with permanent magnets.
 11. The compact dry-running piston compressor according to claim 1, further comprising commutating electronics for controlling the electric motor, the commutating electronics being arranged on a printed circuit board accommodated in or on the second housing section.
 12. The compact dry-running piston compressor according to claim 1, further comprising a relatively flat cover for closing-off an end side of the second housing section.
 13. The compact dry-running piston compressor according to claim 1, wherein the first housing section includes an opening in which the cylinder, formed as a separate component, is releasably attached.
 14. The compact dry-running piston compressor according to claim 1, further comprising inflow ducts arranged in the compressor, the inflow ducts having varying cross-sections to provide different cooling air flows through individual assemblies of the compressor. 